Changestreams orders events from txn by the clusterTime of the commitTransaction. But the order of when commit transaction occurs in shard is orthogonal to the order of when individual ops where issued. For example, in the case of changing the shard key of a document. This will involve deleting document on shardA and inserting the document with the new shard key on shardB under a single transaction. It is possible that commit can happen on shardB first, resulting in the change streams showing the insert first instead of the delete.